Cold Weather Concreting – It’s That Time of Year Again
By Nate Menuez, PE, LEED AP
Senior Structural Engineer, Morrison-Maierle
What exactly is Cold Weather Concreting? The subject rears its head this time of year on every project that has concrete foundations, slab-on-grades, and elevated slabs.
As we all are aware, it is best to have these discussions with the contractor and sub-contractors well before concrete placement actually occurs. The contractor and sub-contractor should have a plan in place prior to the actual placement. However, many times there is a disconnect between general contractor, sub, and even supplier. All too often we hear questions like “Who will provide the blankets?” “Who’s responsible for the external heat?” just to name a few.
The Standard Specifications for Cold Weather Concreting (ACI 306.1-90) defines cold weather as “a period when for more than three successive days the average daily outdoor temperature is below 40 F. The average daily temperature is the average of the highest and lowest temperature during the period from midnight to midnight. When temperatures above 50 F occur during more than half of any 24-hour duration, the period shall no longer be regarded as cold weather.”
Keep in mind, even if we aren’t into to official cold weather protection, short-term protection measures are also required. An example of short-term would be a hard, overnight freeze, overnight snow or rain, amongst others.
Below is the ACI table indicating recommended concrete temperatures at placement, and more importantly, during the cure period. One that always catches me off guard is the allowable drop in temperature in the first 24 hours of removal of external protection.
This is a short summary for a complex topic, so please contact me at firstname.lastname@example.org with questions, comments, or suggestions.